An Experimental and Numerical Thermal Flow Analysis in a Diffuser by Inserting Different Types of Vortex Generators, Part (I)

The present study aims to estimate the Heat Transfer (HT) effectiveness of a diffuser roughened with different configurations of Wing Vortex Generators (WVGs), employing both empirical and numerical approaches. The velocity distribution upstream of the diffuser exhibits a uniform profile, indicating the flow is developing. The WVGs are mounted on the bottom surface of the diffuser. It is noted that the three-pair casing has a higher improvement in HT. The Reynolds number (Re), determined from both the inlet velocity and the diffuser length, falls within the range of ۱۳۲۵۰-۴۳۰۰۰. According to the findings, the Delta-Wing Vortex Generators (DWVGs) cases show more improvement than smooth and Rectangular-Wing Vortex Generators (RWVGs) cases. Numerical results demonstrated that, in comparison to RWVGs, the use of DWVGs produced more durable horseshoe vortices, as evidenced by swirling flows. As a result, the fluid mixing increased and the Thermal Boundary Layer (TBL) shrank. Adding more pairs of vortex generators resulted in a ۵۰% to ۸۲% increase in the friction factor and a ۹۰% to ۱۲۹% increase in the Nusselt number (Nu) for cases with DWVGs compared to the smooth diffuser. For cases with RWVGs, the corresponding increases were ۵۴%–۸۶% for the friction factor (f) and ۳۰%–۶۰% for the Nu. It is also found that the DWVGs exhibit the most significant improvement in the Nu ratio at ۲.۳۷ and the performance evaluation (PEC) criteria at ۱.۹. The PEC seems to be consistently larger than one, for all of the scenarios. This illustrates the benefits of energy conservation by using these particular configurations of wing vortex generator inserts. Additionally, it is essential to mention that the three pairs of DWVGs generate longitudinal vortices similar to a horseshoe shape, while RWVGs produce a swirling flow.

کلیدواژه ها:

Heat transfer enhancement ، Diffuser ، Delta-wing VGs ، Rectangular-wing VGs